Abstract: The Scale-Up Component of the Partnership in Implementation Science for Geriatric Mental Health (PRISM) project proposes an evidence-based physical exercise intervention for older adults who exhibit behavioral and psychological symptoms of dementia (BPSD). The intervention will be delivered in Thai communities through an evidence-based implementation strategy of ?task sharing? among community health workers (CHWs), nurses, primary care physicians, and mental health specialists. In response to the common problem of technical and cultural compatibility between evidence-based interventions and local implementation contexts as well as the uneven local political will for implementing mental health service initiatives, we propose to develop and test an innovative implementation support strategy (i.e., the GTO-ThAI model), based on the evidence-based Getting-to-Outcome model, which will be adapted to Thai settings, to ensure the success of implementation and scaling up of the mental health service for older adults in Thailand. To our knowledge, no previous study has examined the effectiveness of a GTO-ThAI implementation support strategy for delivering clinical interventions for older adults with BPSD in Asia. The proposed evaluation study will conduct a randomized controlled trial with a Hyprid Type 3 design to compare the intervention arm that implements the culturally-adapted GTO model (GTO-ThAI) to deliver implementation support, with a control arm, which receives usual top-down administrative instruction for implementing a policy initiative. Our specific scale-up study aims are to: 1) tailor an evidence-based physical exercise intervention (EBPEI) to fit with Thai local social, cultural, and policy context (Yr 1); 2) develop culturally-informed tools to assess readiness for implementing EBPEI to improve mental health of older adults in local provinces of Thailand (Yr 1); 3) develop the GTO-ThAI implementation support model through a pre- implementation case study and formative evaluation (Yr 2); 4) evaluate implementation strategies and clinical outcomes through a hybrid Type 3 randomized trial to test effectiveness of the GTO-ThAI implementation support strategy for the delivery of EBPEI, compared with the existing standard administrative procedures for delivering the same EBPEI (Yrs 3-4); 5) develop policy recommendations with tools and performance indicators (Yr 5). The proposed scale-up study is expected to generate knowledge and tools essential for further scale-up of mental health services in Thailand, and will contribute significantly to knowledge development within other NIMH program HUBs on going to scale with mental health innovations in LMICs.